130 
POPULAR SCIENCE REVIEW. 
The smallness of the information that can thus he learnt 
from simply placing the finger on an artery has for some time 
past led physiologists to attempt to produce an instrument 
which will make the details of each pulse-beat manifest to some 
sense other than the touch. In elderly men with bald heads 
the anterior branch of the superficial temporal artery is seen to 
take a sinuous course towards the upper part of the forehead, 
and it is possible, without much difficulty, to see its pulsa- 
tions. The beating of a small vessel which runs from the wrist 
to the ball of the thumb is often visible ; and it is said that 
Gralileo constructed the first sphygmoscope (adnsy/ios, “the 
pulse,” and o-kottsu >, “ I see ”), by placing a small light mirror, 
with one edge resting on this artery and the other on the sur- 
face close by, in such a way that the sun’s rays fell upon it, and 
threw the image of the moving beam on a wall some distance off. 
There is, however, a great disadvantage in this method of 
observation, which is that the results arrived at are not perma- 
nent ; so that experiments made at different times cannot be 
compared together as to their results. To obviate this imperfec- 
tion Vierordt constructed a sphyc/mograph (crcfcvyfjLo?, 7 pa<£&>, 
“ I write ”), which by writing on a paper the movements that 
attended its application, rendered comparison easy. The instru- 
ment he employed consisted of a system of two parallel levers of 
the third order, linked together and made excessively sensitive 
by placing sand in counterpoise cups fixed on them. The 
tracings were obtained by making the tips of one of the levers 
scratch a smoked glass plate which moved past it slowly. They 
were found to be very unsatisfactory, as they formed nothing but 
simple up and down strokes of very similar length and general 
appearance, the reason being that the momentum developed by 
the weight of the levers, counterpoises, &c., entirely disguised 
the true movements of the artery, and made the trace completely 
valueless. M. Marey, of Paris, set to work to remedy this 
imperfection, making use of the important principle that a 
definite pressure can be applied on any given spot by a steel 
spring with the introduction of a much smaller weight of ma- 
terial than is necessary to produce the same pressure if no spring 
is employed. He made his lever extremely light ; produced 
the compression of the artery, which is necessary before any 
movement can be imparted, by means of a strong spring, and 
employed a second small spring to counteract any tendency to 
oscillation that might occur. 
Marey’s sphygmograph, as originally constructed by Breguet, 
consists of a long brass frame, which supports both the lever to- 
gether with its accessories, as well as the watchwork and paper 
on which the tracings are recorded. A strong steel spring, 
about four inches long, is attached to this framework near its 
